Golang Convert String to io.Writer?

Question

Is it possible to convert a string to an io.Writer type in Golang?

I will be using this string in fmt.Fprintf() but I am unable to convert the type.

Answer 1

You can't write into a string, strings in Go are immutable.

The best alternatives are the bytes.Buffer and since Go 1.10 the faster strings.Builder types: they implement io.Writer so you can write into them, and you can obtain their content as a string with Buffer.String() and Builder.String(), or as a byte slice with Buffer.Bytes().

You can also have a string as the initial content of the buffer if you create the buffer with bytes.NewBufferString():

s := "Hello" buf := bytes.NewBufferString(s) fmt.Fprint(buf, ", World!") fmt.Println(buf.String()) 

Output (try it on the Go Playground):

Hello, World! 

If you want to append a variable of type string (or any value of string type), you can simply use Buffer.WriteString() (or Builder.WriteString()):

s2 := "to be appended" buf.WriteString(s2) 

Or:

fmt.Fprint(buf, s2) 

Also note that if you just want to concatenate 2 strings, you don't need to create a buffer and use fmt.Fprintf(), you can simply use the + operator to concatenate them:

s := "Hello" s2 := ", World!"  s3 := s + s2  // "Hello, World!" 

Also see: Golang: format a string without printing?

It may also be of interest: What's the difference between ResponseWriter.Write and io.WriteString?